Aluminum alloy sheet excellent in high-speed superplastic formability and process of forming the same

Abstract

An alloy containing 3.0 to 8.0 wt. % of Mg, 0.001 to 0.1 wt. % of Ti, and amounts of Fe and Si (as impurities) as small as 0.06 wt. % or less, the balance being Al and unavoidable impurities, wherein the number per square millimeter of grains of an Al—Fe—Si compound having a diameter of 1 μm or more is 2000 or less, the mean crystal grain diameter is 25 to 200 μm and the elongation is 350% or more as worked at 350 to 550° C. and a strain rate of 10 −2 to 10 0 /s. This alloy may further contain a small amount of Cu, Mn and/or Cr and is formed at 350 to 550° C. and a strain rate of 10 −3 to 10 0 /s. An aluminum alloy sheet with excellent high strain rate superplastic formability and therefore capable of being formed at high temperature and high speed is obtained and the use of this sheet shortens the forming time to improve productivity.

What is claimed is:  
     
         1 . An aluminum alloy sheet with excellent high-speed superplastic formability comprising an alloy containing 3.0 to 8.0% (% by weight, hereinafter the same) of Mg, 0.001 to 0.1% of Ti, controlled amounts of Fe and Si (as impurities) each at 0.06% or less, and the balance being Al and unavoidable impurities, wherein the number per square millimeter of grains of an Al—Fe—Si compound existing in the matrix structure of said alloy and having a diameter of 1 μm or more is 2000 or less, the mean crystal grain diameter is 25 to 200 μm and the elongation is 350% or more as worked at a temperature range of 350 to 550° C. and a strain rate of 10 −2  to 10 0 /s.  
     
     
         2 . The aluminum alloy sheet with excellent high-speed superplastic formability according to    claim 1   , wherein said alloy further comprises 0.05 to 0.50% of Cu.  
     
     
         3 . The aluminum alloy sheet with excellent high-speed superplastic formability according to    claim 1    or    claim 2   , wherein said alloy further comprises either one or both of not more than 0.10% of Mn or not more than 0.1% of Cr.  
     
     
         4 . A method for forming the aluminum alloy sheet with excellent high-speed superplastic formability according to    claim 1   ,    claim 2   , or    claim 3   , wherein the aluminum alloy sheet is formed at a strain rate of 10 −3  to 10 0 /s and at a temperature between 350 to 550° C.